How do you do them? I have the seeds and stuff, but I notice people saying that they are great xp. What do I have to do with them and how can I get the most xp out of them?

You plant em. Pay the farmer. Wait for 15 hours. Check them. Then Harvest fruit's. Chop it down. Grow another one. Repeat.

You first have to plant the seeds into a plant pot, then water it. It will grow into a sapling ( takes 1-2 minutes at most). After that you must go to a fruit tree patch, clean the patch then use the sapling on the patch.If the payment items are cheap/easy to obtain, I'd say pay the farmer(less risk of your trees dieing).